1. Field of the Invention
This invention relates to lens control systems suitably used for video cameras and electronic still cameras and, more particularly, to lens control in wide-macro region.
2. Related Background Art
Recently, video apparatuses such as video cameras and electronic cameras have been developed remarkably, and particularly various functions are provided as standard functions such as autofocus (AF), autostop (AS), automatic white balance control, zooming and macro-photography to improve the performance and operability.
Concerning the autofocus, it is now becoming a main system to detect the sharpness of object image from video signal obtained through photoelectric conversion of optical signal from an image sensor element or the like and effect focus control through focusing lens position control such as to provide for a maximum sharpness of the image.
The sharpness is usually evaluated in terms of the high frequency component level of a video signal extracted by a band-pass filter (BPF) or the detection level of blur width (i.e., width of an edge portion of object image) of a video signal extracted by a differentiating circuit or the like.
When a usual object is photographed in an out-of-focus state, the high frequency component level is high, while the blur width is large. When perfect focus is obtained, the high frequency component level and blur width respectively have maximum and minimum values. When the sharpness is low, the focusing lens is driven at as high speed as possible in a direction to increase the sharpness, and as the sharpness is increased it is slowed down to be stopped accurately at a peak of sharpness. This focusing system is commonly termed the mountain-climbing autofocusing (AF) system.
With the adaptation of this autofocus function, the operability of particularly video cameras or the like for taking motion pictures is revolutionally improved, and the function is currently a prerequisite.
With operability improvement attained with adaptation of the AF system and also for a purpose of increasing the scope and functions of photography to be able to meet many more photographic conditions, zoom lenses are adopted as standard elements to permit tele-macro photography, i.e., photography in tele-macro region. They permit focusing of closer objects with extension of the movable range of a conventional front focusing lens to the macro side. For example, there are many proposed cameras with zoom lenses having a function of macro-photography. In a well-known example of such camera, a first group lens (i.e., front lens) effects focusing, and second and third group lenses effect zooming.
In this case, when an object gets closer and to be in a macro distance beyond a distance control range, in which focusing can be effected by the first group focusing lens, the focusing lens can no longer effect focusing, and in such a circumstance the second and third group lenses which effect zooming are moved relatively to effect the shortest range photography (macro-photography).
For macro-photography, lenses are moved from the tele- or wide-end of the zoom lens.
With prior art cameras, however, the focusing lens remains under auto-focus control even when it is detected that the zoom lens is in wide-macro region, or the position of the focusing lens at the instant of reaching of the wide-macro region by the zoom lens is held even when the focusing lens is stopped. This means that the object distance range in the wide-macro region is from the immediate lens front to the focusing lens position, and depending on the focusing lens position the range of focusing by movement of a compensator lens is affected. Therefore, in many cases it is optically impossible to effect focusing from infinity up to the immediate lens front.
Further, continuous lens operation may cause image magnification changes and also increases power consumption.
In a further aspect, in the wide-macro region the focusing is effected by operating the zoom lens. This control is different from focusing in the normal region, and usually focusing in the wide-macro region is done manually. This is a sacrifice in view of the operability improvement.
In the meantime, there is commonly termed power wide-macro focusing which is proposed for such case as when direct manual zoom lens operation is impossible. In this case, wide-macro focusing is effected by driving the zoom lens with a switch input operation.
However, autofocusing is desired from the standpoint of operability. In view of autofocusing in the wide-macro region, it may be considered to perform mountain climbing AF control of the zoom lens according to focus detection information in the wide-macro region. However, since the focusing is done by different control systems in the wide-macro region and in the normal region, the mountain climbing AF control will deteriorate the response of AF operation when normal AF operation is restored after the end of the wide-macro AF operation in the wide-macro region.
Further, when the focusing lens driving motor is operated during wide-macro AF operation, such serious problems as generation of drive noise, increase of power consumption and increase of other noise are presented, although the focusing itself may not be affected.
Further, in an operability aspect, automation of various operations is demanded very strongly in a system having both tele- and wide-macro AF functions. In a system, in which the focusing is done automatically in the normal region but is done manually in the macro region, the operability is unsatisfactory, and it is impossible to make use of the features of AF function in the normal region.
For permitting autofocusing in the wide-macro region, it may be considered to let the zoom lens be controlled by mountain climbing AF control according to focus detection information. However, since focusing is done by different control systems in the wide-macro and normal regions, in such case as when front focusing lens is in a tele-macro region of 0.6 to 1.2 m at an instant of start of wide-macro AF operation in the wide-macro region a phenomenon of failure of focusing of a distant object is liable due to optical limitations. This is a very serious problem in view of overall automation of focusing of the system.